STABILIZED HIGH TEMPERATURE OXIDES BY CVD

ZIRCONIA (ZRO(2) AND HAFNIA HFO(2)) HAVE BEEN IDENTIFIED AS MAJOR ELEMENTS IN THE DEVELOPMENT OF COMPONENTS WHICH CAN OPERATE AT ULTRA HIGH TEMPERATURES (3000 - 4000F AND ABOVE). BOTH MATERIALS ARE VERY REFRACTORY (MELTING TEMPERATURE ABOVE 4800F), STABLE COMPOUNGS, THAT HAVE HIGH CHEMICAL INERTNESS AND LOW VAPOR PRESSURE AT HIGH TEMPERATURE. BOTH HAVE LONG BEEN USED IN BULK FORM AS OXIDATION RESISTANT MATERIALS ABOVE 1800C (3272F). FOR CARBON AND OTHER COMPOSITE MATERIALS TO OPERATE AT 3000-4000F AND ABOVE A METHOD OF VAPOR DEPOSITING THESE MATERIALS, AS SURFACE COATINGS OR INFILTRANTS, WILL BE REQUIRED. HFO(2) AND ZR0(2) CAN BE DEPOSITED BY CHEMICAL VAPOR DEPOSITION (CVD) BUT THE DEPOSITED MATERIALS SUFFER FROM THE SAME FLAW AS THE BULK MATERIALS: A MARKED PHASE CHANGE ACCOMPANIED BY A VOLUME CHANGE AT TEMPERATURES (TRANSITION TEMPERATURE) 1000-2000C BELOW THE MELTING TEMPERATURE. THIS TYPICALLY RESULTS IN CREACKING AND SPALLING. IN HOT PRESSED MATERIALS THIS PHASE CHANGE CAN BE VIRTUALLY ELIMINATED BY THE ADDITION OF A STABILIZER. TESTS AT ULTRAMET HAVE SHOWN CONCLUSIVELY THAT THESE MATERIALS DEPOSITED BY CVD WILL NEVER OPERATE TO THEIR FULL POTENTIAL ABOVE THE TRANSITION TEMPERATURE UNLESS A MEANS IS DEVELOPED TO INHIBIT THIS PHASE CHANGE. BY AN INNOVATIVE APPLICATION OF CVD ULTRAMET PROPOSE TO DEMONSTRATE THE FEASIBILITY OF STABILIZING CVD HF0(2) AND/OR ZRO(2).